There are many applications where amounts of money are kept in unmanned facilities that are open to public access. For example, cash-operated devices such as vending machines and pay telephones are available to the public and accrue varying amounts of cash as they dispense goods or services to customers. These machines periodically are serviced to remove the money and, in the case of vending machines, to replenish the supply of products. Persons authorized to service pay telephones or vending machines must carry keys permitting access to the coin box or other receptacle receiving money paid into the machine. Pay telephone coin boxes are serviced by a collector who periodically visits each pay phone. The collector unlocks an outer door to the phone using a key for that purpose, and then removes the coin box from within the phone and substitutes an empty coin box. If the collector is allowed to carry one or more master keys for servicing a number of telephones, the risk of loss by theft or misappropriation of a single key is apparent. On the other hand, requiring the collector to carry a separate key for each pay phone represents a significant inconvenience, particularly in areas such as airport terminals where large numbers of pay phones are located. Furthermore, the risk of loss through theft or misuse of individual keys still exists.
Automated teller machines (ATMs) are another example of machines containing cash and requiring periodic access for replenishing the cash supply or maintaining and repairing the machines. Because ATMs are capable of containing large amounts of money relative to most vending machines, they are more inviting targets for theft. For this reason, the cash within an ATM is contained within a small vault integral with the ATM and typically accessible only through a vault door having a combination lock, sometimes combined with a key access, for opening the vault door. Portions of the electronic controls for the ATM also may be located within the vault to prevent unauthorized cash dispensing by tampering with control circuits. Generally speaking, the cash within a locked ATM is secure from any unauthorized activity short of safecracking.
The need for periodic access to the vault of an ATM machine to replenish the cash supply, or to service equipment within the vault, constitutes a weak link in ATM security. If vault access is available only to technicians possessing the proper key or numerical combination to open the vault door, those technicians are vulnerable to being hijacked and forced to hand over the key or divulge the combination to open the vault. Furthermore, job turnover of ATM technicians makes it impractical to give each technician the combinations of ATM vaults, because of the need to reset those combinations whenever the technician left the job. For the same reason, key-only access to ATM vaults presents a problem when the technician leaves the job, due to the risk that the technician may not return the keys or may make an unauthorized copy of the keys while employed. Further yet, security considerations rule against allowing any technician to carry master keys capable of unlocking the vaults in a number of different ATMs, due to the risk of great loss if such master keys were stolen or otherwise came into the wrong hands.
Prior-art techniques are known for providing keyless access to ATMs or other machines containing significant amounts of cash. These techniques generally require an electronic link between the machine and a central office, and an arrangement for unlocking the vault whenever the proper signal arrives from the central office. To avoid the cost of providing dedicated lines between the central office and a great number of ATMs, these prior-art techniques usually rely on the public telephone network and a modem associated with each ATM, in order to communicate between the central office and a selected ATM. While these techniques relieve the service technician of the need to carry either access keys or combinations for the ATM vaults, it still leaves the technician subject to being hijacked by robbers who will then coerce the technician to request access from the central office. On a more sophisticated level, the use of conventional telephone lines for transmitting access signals to ATMs makes those signals subject to interception by wiretapping, leading to the fear that the access signals may be analyzed and then used by others for unauthorized access to ATM vaults. Moreover, the dial-up telephone line required for each ATM is an ongoing expense to the bank or other agency sponsoring the ATM.